A.c. voltage regulator with photo-responsive control means



NOV. 8, 1966 LAKSHMANAN ET AL 3,284,698

A.C. VOLTAGE REGULATOR WITH PHOTORESPONSIVE CONTROL MEANS Filed March 11, 1964 35 our 7& vor'a 2% [0%1S/7/770/70/7 1w fiomofi f. And/0J6 WW INVENTORS J/ BY KM United States Patent 3,284,698 A.C. VOLTAGE REGULATOR WITH PHOTO- RESPONSIVE CONTROL MEANS Tavorath K. Lakshmanan and Roman I. Andrushkiw, Newark, N.J., assignors, by mesne assignments, to Weston Instruments, Inc., a corporation of Delaware Filed Mar. 11, 1964, Ser. No. 351,180

4 Claims. (Cl. 323-75) This invention relates to voltage stabilizing circuits and more particularly to voltage stabilizing circuits for developing an output voltage which remains substantially constant with relatively large variations in the input voltage.

Voltage stabilizing circuits employing bridge networks are known. Such networks often employ fixed and nonlinear resistors. In a typical operation of such circuits, the bridge output voltage is algebraically added to the input voltage, or to a voltage directly proportional to the input voltage, so that when the input voltage increases, the bridge output voltage decreases, and vice versa, thereby maintaining the output voltage from the stabilizing circuit substantially constant.

Although stabilizing circuits of the foregoing character are useful, they do not afiord the degree of stability or regulation required in those applications where it is essential that the output voltage from the stabilizing circuit deviates from a predetermined level by only minute amounts.

Consequently, it is an object of the present invention to provide a stabilizing circuit providing an output voltage which varies insignificantly with relatively large variations in the input voltage.

A further object of this invention is to provide new and improved stabilizing circuits which respond very rapidly even to minute changes in the input voltage, which are very eflicient, and which provide improved regulation over a wider range of input voltage than has been previously possible.

The foregoing and other apparent objects of this invention are accomplished by providing new and improved stabilizing circuits of the type which employ bridge networks, each network comprising at least one light emissive element and a corresponding light-responsive, variable resistance element, such as a photoconductor. The light emissive element is energized by the input voltage or by a voltage representing the input voltage. When the input voltage varies, the output light and the resistance of the photoresponsive element vary correspondingly to provide a bridge output voltage which, when algebraically added to the input voltage, results in an output voltage which is substantially free from variations.

Further objects of this invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a simplified stabilizing circuit in accordance with this invention for regulating a variable direct-current voltage.

FIGURE 2 is a stabilizing circuit in accordance with this invention for regulating a variable alternating-current voltage.

FIGURES 3 through 5 are variations of the embodiment shown in FIGURE 2.

Referring to FIGURE 1, the bridge network includes two resistors 11 and 12 in its two opposite arms and two variable-resistance, light-responsive elements 13 and 14 in its other pair of opposite arms. Elements 13 and 14 may be commercially available photoconductors. Across one diagonal of the bridge is connected a DC. supply source E The output voltage of the bridge E,

is developed across resistor 15 forming the other diagonal of the bridge. The input voltage to be regulated is applied to input terminals 20, 21 and the regulated output voltage is derived from output terminals 22, 23. A light emissive element, such as a lamp 24, is connected across input terminals 20, 21. A wire 25 connects terminals 20 and 22 whereas terminals 21 and 23 are connected through the resistor 15. Within a housing (not shown), the physical arrangement of the various elements is such that light emitted from lamp 24 reaches both photoconductors 13 and 14.

A typical operation of the embodiment shown in FIGURE 1 will be illustrated with a numerical example. Assume that the input voltage E is 115 volts and that it is desired that the output voltage E be maintained at 115 volts. The various components forming the bridge network will be selected so that the bridge is balanced when the input voltage is 115 volts. In this case, E equals E because E, is equal to zero. Now assume that E increases to 130 volts. This voltage rise causes lamp 24 to emit more light. This increased light decreases the resistance of photoconductors 13 and 14, the bridge becomes unbalanced, and a voltage E, is developed across resistor 15. If the various components are properly selected, E will be 15 volts so that the output voltage will be again E =130-15=115 volts.

. In the case when the input voltage decreases, say from 115 volts to volts, the output light decreases, the resistance of photoconductors 13 and 14 increases, and the bridge again becomes unbalanced but in an opposite direction so that now the output voltage will be E =100+15=115 volts.

In the embodiment shown in FIGURE 2, the bridge circuit 10 is of the diilerential type. For isolation purposes, the input voltage E is applied to the primary winding 31 of an isolation transformer 30 having a centertapped secondary winding 32 and another secondary winding 33. Across secondary winding 32 are connected in series a photoconductor 34 and a resistor 35 having a junction 36. Between junction 36 and the center tap 37 on the secondary winding 32 is connected an output resistor 38. As will be appreciated by those skilled in the art, the secondary winding 32 and the elements 34 and 35 form what is known as a difierential bridge. To energize a lamp 39, the other secondary winding 33 is connected through a current limiting resistor 40 to the the lamps input terminals. Again, the regulators output voltage is the algebraic sum of the input voltage E and the bridge output voltage E across resistor 38. The operation of the embodiment shown in FIGURE 2 is similar to that described in conjunction with the embodiment shown in FIGURE 1. For example, for the numerical values previously given, when the input voltage is volts the bridge is balanced, E is equal to zero, and E is equal to E When E increases to volts, the voltage across the secondary winding 33 increases proportionately, more light is produced by lamp 39, the resistance of the photoconductor 34 decreases, the differential bridge becomes unbalanced, and output voltage E equals to 15 volts. The phase of E however, is opposite to the phase of the input voltage. The output voltage E is then equal to 130-15=115 volts.

In one model of the embodiment of the circuit shown in FIGURE 2, the photoconductor 34 was of type RCA 7163 and the lamp 39 was a miniature incandescent lamp GE857, the illumination of which is dependent on the R.M.S. value of the voltage thereacross. Since the reactance of the photoconductive cell 34 is negligible, there is no appreciable distortion or shift in the phase angle of E with respect to E In the remaining embodiments shown in FIGURES 3 3-5, for simplicity, similar reference characters are used to denote similar parts. In FIGURE 3, the lamp 39 forms one arm of the bridge. A resistor 42 is inserted in series with the lamp and another resistor 43 is inserted in series with the photoconductor 34 as shown.

' For the above given type lamp and photoconductor and for an output resistance of 100K connected across the output terminals 44, 45, the following resistance values in ohms were chosen for best regulation: Resistor R38=3,000; and 1143 240- For the embodiment shown in FIGURE 3, Table I shows the percent variation in the output voltage E for variations in input voltage E from 100 to 130 volts.

TABLE I. EFFEOT OF VARIATION IN INPUT VOLTAGE Em in E0 ut O ut Percent Var iation TABLE II.EFFEOT or VARIATION IN INPUT I FREQUENCY 0 ut a ut Percent m Variation Table III shows the percent variation in output voltage E corresponding to a change in the ambient temperature from 25 to C. for a constant input voltage of 110 volts.

TABLE III.EFFECT OF VARIATION IN AMBIENT TEMPERATURE Ein T C. Eout Percent Variation c ut As will be appreciated, the performance of a given stabilizing circuit will depend on the type of photoconductor and lamp employed. For any combination of photoconductor and lamp, by proper selection of the resistance'values of resistors 40, 38, 42 and 43, the stabilizing circuit will operate efliciently and reliably. The choice of these resistance values is determined by the following design considerations. Resistor 40 limits the amount of power delivered to the lamp 39. For a desired stabilized output of 115 volts, it is adjusted so that at an input voltage of 100 volts at the transformer primary winding 31, the lamp draws approximately one-half of its rated current. For the lamp used (GE 857), the actual current ranged from 70 to 93 milliamps for an input voltage range between 100 and 130 volts. The choice of resistor 42 depends on the resistance of the photoconductor 34 and is selected to be approximately equal to the resistance of the illuminated photoconductor when the input voltage is, 100 volts. Resistor 38 is selected on the basis of maximum power output and is made equal to the source resistance or approximately one-half of resistor 42.

Resistor 43 limits the nonlinearity of the bridge output voltage E, and is experimentally adjusted so that the rate of change of E is substantially equal to the rate of change of the input voltage in the desired operating range. For a further discussion of the operation and design criterions of the embodiment shown in FIGURE 3, reference is 4- made to applicants publication in the Review ofScientific Instruments, April 1963, pages 433, 435.

Obviously many variations are possible as will be apparent to those skilled in the art. For example, FIG- URE 4 differs from the previous embodiments in that the lamp 39 is connected across the input line. In FIGURE 5, the lamp is positioned across one diagonal of the bridge. One photoconductor is placed in one arm of the bridge and another photoconductor in an opposite arm of the bridge as shown instead of directly being added to E The bridge output voltage E, is added to a voltage E' across a secondary Winding 51 wound on transformer 30, the voltage E' varying directly With E Consequently, although the present invention has been shown and described with reference to particular embodiments, various changes and modifications obvious to those skilled in the art are deemed to be within the spirit, scope and contemplation of the invention.

What is claimed is:

1. A voltage stabilizing circuit for providing a stabilized output voltage with relatively large excursions in an input voltage, said stabilizing circuit comprising:

a pair of input terminals for receiving said input voltage,

a bridge network,

means coupling said input terminals to said bridge network for energizing said bridge network with a voltage varying in correspondence with said input voltage,

a light responsive element connected in at least one arm of said bridge network,

said light responsive element having an electrical resistance which varies inversely with the intensity of impinging light, I

a light emitting element for illuminating said light responsive element;

means coupled to said light emitting element to energize said light emitting element by a voltage varying in correspondence with said input voltage, so that when the input voltage decreases the output light decreases in correspondence with said input voltage and when the input voltage increases the output light increases in correspondence with said input voltage;

a pair of output terminals for providing said stabilized voltage, and means including an impedance element connected across a diagonal of said bridge network for coupling said input terminals with said output terminals.

7 2. A voltage stabilizing circuit for providing a stabilized output voltage with relatively large excursions in an input voltage, said stabilizing circuit comprisingi a pair of input terminals for receiving said input voltage,

a bridge network,

a transformer having a primary winding, a first secondary Winding and a second secondary Winding, said first secondary winding having a center tap,

a first output terminal,

means including a light responsive element connected between said first output terminal and one end of said first secondary winding, I

said light responsive element having an electrical resistance which varies inversely with the intensity of impinging light,

means including a light emitting element connected between said first output terminal and the other end of said first secondary winding, ,7 said light emitting element being positioned for illuminating said light responsive element, means connecting said second secondary winding to energize said light emitting element,

a constant resistance element connected between said center tap and said first output terminal,

means connecting one end of said primary winding to said center tap,

a second output terminal, and means connecting said second output terminal with the other end of said primary winding. 3. A voltage stabilizing circuit for providing a stabilized output voltage with relatively large excursions in an input in correspondence with said input voltage;

a bridge network having resistive arms of fixed and non-linear resistances;

a light responsive element in at least one arm of said bridge network, said light responsive element having voltage, said stabilizing circuit comprising: 5 a resistance which varies inversely with impinging a pair of input terminals for receiving said input light,

voltage, a light emitting element for illuminating said light rea bridge network, sponsive element, said light emitting element being means coupling said input terminals to said bridge netenergized by a voltage varying in correspondence with work for energizing said bridge network with a volt- 10 said input voltage whereby when the input voltage age varying in correspondence with said input voltage; decreases in correspondence with said input voltage, a light responsive element connected in at least one the output light decreases and when the input voltage arm of said bridge network, said light responsive eleincreases in correspondence with said input voltage, ment having an electrical resistance which varies inthe output light increases, versely with the intensity of impinging light; means energizing said bridge net work with a voltage a light emitting element for illuminating said light corresponding to said input voltage,

responsive element, said light emitting element being said bridge network providing a bridge output voltage connected in at least another arm of said bridge net- Which varies inversely with the input voltage of said work; stabilizing circuit, and means coupled to said light emitting element to energize an output circuit including output terminals for adding said light emitting element by a voltage varying in said bridge output voltage to a voltage corresponding correspondence with said input voltage so that when to said input voltage thereby providing to said output the input voltage decreases, the output light decreases terminals a substantially constant voltage. in correspondence with said input voltage and when the input voltage increases, the output light decreases References Cited y the Examiner UNITED STATES PATENTS a pair of output terminals for providing said stabilized voltage, and means including an impedance element 5 2: et connected across a diagonal of said bridge network 3,040,241 6/1962 Wunderman.

for coupling said input terminals with said output terminals.

4. A voltage stabilizing circuit for providing a substantially constant output voltage with relatively large excursions in an input voltage said stabilizing circuit comprising:

JOHN F. COUCH, Primary Examiner.

A. D. PELL'IN EN, Assistant Examiner. 

1. A VOLTAGE STABILIZING CIRCUIT FOR PROVIDING A STABILIZED OUTPUT VOLTAGE WITH RELATIVELY LARGE EXCURSIONS IN AN INPUT VOLTAGE, SAID STABILIZING CIRCUIT COMPRISING: A PAIR OF INPUT TEMINALS FOR RECEIVING SAID INPUT VOLTAGE, A BRIDGE NETWORK, MEANS COUPLING SAID INPUT TERMINALS TO SAID BRIDGE NETWORK FOR ENERGIZING SAID BRIDGE NETWORK WITH A VOLTAGE VARYING IN CORRESPONDENCE WITH SAID INPUT VOLTAGE, A LIGHT RESPONSIVE ELEMENT CONNECTED IN AT LEAST ONE ARM OF SAID BRIDGE NETWORK, SAID LIGHT RESPONSIVE ELEMENT HAVING AN ELECTRICAL RESISTANCE WHICH VARIES INVERSELY WITH THE INTENSITY OF IMPINGING LIGHT, A LIGHT EMITTING ELEMENT FOR ILLUMINATING SAID LIGHT RESPONSIVE ELEMENT; MEANS TO COUPLED TO SAID LIGHT EMITTING ELEMENT TO ENERGIZE SAID LIGHT EMITTING ELEMENT BY A VOLTAGE VARYING IN CORRESPONDENCE WITH SAID INPUT VOLTAGE, SO THAT WHEN THE INPUT VOLTAGE DECREASES THE OUTPUT LIGHT DECREASES IN CORRESPONDENCE WITH SAID INPUT VOLTAGE AND WHEN THE INPUT VOLTAGE INCREASES THE OUTPUT LIGHT INCREASES IN CORRESPONDENCE WITH SAID INPUT VOLTAGE; A PAIR OF OUTPUT TERMINALS FOR PROVIDING SAID STABILIZED VOLTAGE, AND MEANS INCLUDING AN IMPEDANCE ELEMENT CONNECTED ACROSS A DIAGONAL OF SAID BRIDGE NETWORK FOR COUPLING SAID INPUT TERMINALS WITH SAID OUTPUT TERMINALS. 